This invention relates to digital electronic musical instruments.
For use in prior art electronic musical instruments various means have been proposed to obtain desired musical tone waveforms. One such proposal is disclosed in U.S. Pat. No. 3,882,751 to Norio Tomisawa dated May 13, 1975. According to the waveform memory read-out system disclosed in this patent, there is provided a frequency information memory device adapted to store frequency information data F corresponding to or proportional to the tone pitches of respective keys of a keyboard of the musical instrument and the frequency information memory device is addressed by a key information representing a depressed key. The read out frequency information F is repeatedly accumulated at a definite speed to form an accumulated valve qF (where q=1, 2, 3, . . . ) which is utilized in a waveform memory device which stores amplitude values at successive sampling points of one period of a desired musical tone waveform to successively read out the amplitude values at successive sampling points thereby forming a desired musical tone waveform.
Another proposal is disclosed in U.S. Pat. No. 3,821,714 to Norio Tomisawa dated June 28, 1974. In this patent, a harmonic synthesizing system is disclosed wherein a fundamental wave (fundamental tone) corresponding to the tone pitch of a depressed key and harmonic components thereof (harmonics) are generated. After multiplying these fundamental wave and harmonic components by corresponding amplitude coefficients, their products are synthesized to obtain a musical tone.
In order to produce musical tones rich in naturality, however, such prior art systems have the following problems. More particularly, in the former electronic musical instrument of the waveform memory device read out type, when the waveform stored in the waveform memory device is once set, it is impossible to change the waveform that is the tone color because the shape of the read out musical tone waveform is always the same. To solve this problem, it has been proposed to provide a plurality of waveform memory devices which store musical tone waveforms having different shapes so as to selectively access these plurality of waveform memory devices thereby changing the shape of the waveform of the generated musical tone. However, an electronic musical instrument having such construction is complicated because it requires a number of waveform memory devices.
Where it is desired to vary with time the tone color as the time elapses after depression of a key just like a natural musical instrument, there is a difficult problem that it is not simple to vary with time the waveform read out of the waveform memory device.
Furthermore in the latter electronic musical instrument of the harmonic synthesizing type, in order to vary the shape of the synthesized musical tone waveform, it is necessary to prepare a large number of amplitude coefficients multiplied with the fundamental wave and the harmonic components thereof. As a consequence, it is necessary to increase the number of the memory devices for storing a large number of the amplitude coefficients.